1. Field of the Invention
The present invention relates to an image forming apparatus using an electrophotographic process, such as a facsimile machine, a printer, or a multifunctional machine combining functions thereof, and more particularly, to a technology to discharge heat and prevent moisture generated in the image forming and image fixing devices employed in the image forming apparatus.
2. Discussion of the Related Art
With recent advances in electrophotographic image forming apparatuses such as high-speed multicolor apparatuses, demand for greater compactness has also become acute. As a result, parts or components have come to be mounted more closely together and the problem of cooling these components has become a critical issue. In particular, with the development of high-speed multicolor machines, the self-heat generation amount in the imaging unit (i.e., image forming device) has increased, necessitating heat discharge or cooling so that toner inside the image forming device does not melt or solidify. With the trend toward greater compactness, a fixing device, a transfer device, and the image forming device are now mounted close to each other, which may give an adverse effect to these peripheral devices due to the heat generated by the fixing device.
In order to solve such problems, conventionally, there are image forming apparatuses capable of cooling the fixing device and the proximally provided image forming device (e.g., JP-2006-078534-A, JP-2006-195357-A, and JP-2008-250284-A). For example, JP-2006-078534-A discloses an image forming apparatus which includes a ventilation duct having an air passage to cool a controller board of the fixing means and another air passage to cool a portion around the image carrier, thereby cooling the controller board and the image carrier and their peripheral portions.
The image forming apparatus disclosed in JP-2006-078534-A including the ventilation duct requires a duct space from each air inlet to the objects to be cooled. Thus, the machine size needs to be enlarged and the requirement for greater compactness cannot be met.
As a solution to the above heat discharge problem, it is conceivable to provide an exhaust fan above the fixing device to discharge moist, hot air directly generated by the fixing device to an outside of the apparatus body. However, if, in a case of an image forming apparatus of a vertical-sheet-conveyance type, in which a printed sheet is discharged onto an upper surface of the apparatus, or a type provided with a sheet duplex unit for duplex printing, and a compact and ventilation-effective, axial-flow fan is arranged as an exhaust fan above the fixing device, the exhaust direction of the axial-flow fan is along the fan axis. Thus, if the exhaust direction is with the same as a sheet conveyance path, the exhaust fan lies across and blocks the sheet conveyance path. Even though the exhaust fan is provided parallel to and offset from the sheet conveyance path so as not to block the sheet conveyance path, the width of the exhaust fan intersects the sheet conveyance path, thereby generating wasted space, which is inconsistent with the requirement of greater compactness.
Accordingly, to meet the requirement of greater compactness, without providing the exhaust fan (axial-flow fan) such that the exhaust direction is the same as or parallel to the sheet conveyance path, it is conceivable that, in order to avoid wasted space, the axial direction of the exhaust fan is provided either perpendicular or at a predetermined angle to the sheet conveyance path, thereby achieving a more compact machine size. However, with such an arrangement, there may occur a problem of condensation, in which parts or components-provided downstream of the exhaust fan in the exhaust direction tend to be exposed to hot, humid wind generated when the fixing device heats the moisture-absorbing sheet, and after the main power is turned off and the exhaust fan is stopped, highly moist air around the parts or components is cooled by outside air below the dew point, whereby condensation occurs. If condensation does occur, water droplets fall from the parts or components and adhere to lower-lying components such as the exhaust fan, the upper surface of the fixing device, the sheet conveyance path and the like may cause various disadvantages. In particular, if the droplets are attached to the sheet conveyance path, the sheet becomes wet in the next conveying operation, risking defective results such as wet output images and defective sheet conveyance due to sticking of the sheet to the sheet conveyance path.
For these reasons, a need exists for an image forming apparatus capable of effectively discharging the heat and moisture generated in the fixing device and preventing condensation around the sheet conveyance path, without increasing the overall size of the apparatus.